This invention relates generally to drive systems. More particularly, it relates to an assembly which is adapted to drive the accessories in a vehicle. In such an adaptation, the assembly absorbs some of the energy which normally would be lost when the vehicle brakes are applied or the engine decelerates, and uses this energy to help drive the accessories.
Modern vehicle engines are called upon to drive an increasing number of accessories. As much as twenty-five percent of the engine brake horsepower available may be required to drive them. Thus, the efficiency of the accessory drive system is important in so far as it relates to fuel economy.
The ideal condition would be to drive the accessories at a constant speed. This is impractical in an automotive vehicle. Generally, an accessory drive system drives accessories at some speed which is a linear function of engine speed. At low engine speeds, for example at engine idle speed, it may be necessary to increase the size and capacity of the accessories. Similarly, at high engine speeds, the accessories may be driven too fast for efficient operation.
Copending U.S. application Ser. No. 90,191 filed Nov. 1, 1979 discloses an accessory drive assembly incorporating a planetary gear set and a power train. The carrier is driven by the engine crankshaft of an associated vehicle. The ring gear provides the driving torque for vehicle accessories. The sun gear is driven by the tailshaft of the vehicle through the power train.
With the engine running at idle and the vehicle stopped, the planetary gear set develops an output speed which is some multiple of engine speed. When the vehicle begins moving, the sun gear is driven at some multiple of tailshaft speed. Thus, assembly output speed increases at a rate slower than that of engine speed. The result is a compression of the assembly output speed range as compared with the engine speed range, and an improvement in the operating efficiency of the accessory drive assembly.
However, considerable energy is lost during the period in which the vehicle brakes are applied. Indeed, energy distribution in a passenger car during a city/highway EPA cycle is such that as much as fourteen percent of the vehicle's brake horsepower may be dissipated in braking. If some of this energy could be applied to help drive the vehicle accessories, overall operating efficiency would be improved even more, with a resulting improvement in fuel economy.
The accessory drive assembly disclosed in the aforementioned U.S. application Ser. No. 90,191 inherently is unable to utilize energy lost in braking. Thus, there remains a need in the art for a simple, inexpensive accessory drive system with an output speed range that is compressed as compared with its input speed range, and with the capability of absorbing and using some of the energy which otherwise would be lost when the vehicle brakes are applied or the engine is decelerated.